In the prior art, an electronic device, for example, a surface-mount crystal oscillator is configured by mounting a crystal resonator 13 and circuit components 14 on a principal surface of a base board 10 and covering the base board 10 with a metal cover 9 from the upside as shown in FIG. 9.
Here, in order to install the metal cover 9 in the base board 10, protrusions 11 are provided on the side surface of the metal cover 9, and bulging portions (claw) 12 extend downwardly from the protrusions 11. In addition, the protrusions 11 abut on the outer circumferential surface of the base board 10, and the bulging portions 12 extending downwardly from the protrusions 11 are inserted into the notches 18 formed on the side surface of the base board 10, so that the metal cover 9 is elastically retained in the side surfaces of the base board 10 as shown in FIG. 10, and, the metal cover 9 and the base board 10 are fixed by soldering (See Japanese Patent Laid-Open Publication No. 2000-165177, hereinafter referred to as Reference 1).
In this regard, in the prior art, as an example of the claw for engaging/securing the metal cover 9 with the base board 10, there has been proposed a technique in which a fitting claw 12a is formed in the cover 9 in a substantially L-shaped bent and widened to the outer side and is fitted and locked to the fitting trench 18a formed in the base board 10 as shown in FIG. 11A. Alternatively, as shown in FIG. 11B, a substantially L-shaped bend portion having elasticity is formed in a center portion of the fitting claw 12b formed in the cover 9, the fitting claw 12b is inserted into the fitting hole 18b formed in the base board 10, so that the cover 9 is locked to the base board 10. Alternatively, as shown in FIG. 11C, the fitting claw 12c formed in the cover 9 is configured in a Y-bend shape having a gap g in its center so as to provide elasticity in an outwardly widened direction, so that the cover 9 is locked to the base board 10 (See Japanese Utility Model Laid-Open Publication No. 6-79185, hereinafter referred to as Reference 2).
However, in such a type of electronic device, for example, a crystal oscillator, after the fitting claw provided in the cover is inserted into the fitting hole provided in the base board, the cover is fixed to the mount board by soldering the peripheral of the cover. For this reason, it is difficult to obtain a perfectly lead-free device. In addition, the solder used to fix the cover may be re-molten during a reflow work when a user mounts the device on the mount board, so that the cover may slip from the base board.
In addition, in order to achieve perfect engagement/securing between the cover and the printed (base) board, it is necessary to change a design of the shape of the fitting claw provided in the cover and the like to match the printed board to be engaged/secured. Therefore, it is significantly difficult to commonly use the ready-made cover in various types of printed boards.